Supermassive black holes might slowly suffocate galaxies. The suggestion runs counter to astronomers’ notion that galaxies stop forming stars when they run out of cold gas. But researchers have found a cache of galaxies loaded with cold gas that aren’t making stars. The team’s observations suggest that the galaxies’ central black holes stirred up the gas and shut down the stellar assembly lines.

Over the last decade, astronomers have learned that black holes can drive the fates of entire galax...